1. Field of the Invention
The present invention relates to integrated circuits, and more specifically to high voltage circuits implemented using low voltage transistors of reduced number of voltage specifications.
2. Related Art
Integrated circuits are generally provided a supply voltage, and it is some times desirable that a high (compared to voltage specification of a transistor, as described below) voltage be provided for the supply voltage. For example, using a high supply voltage generally provides a correspondingly high signal to noise ratio (SNR), typically leading to less susceptibility to noise in processing input signals. Integrated circuits with high supply voltage may be referred to as high voltage circuits.
Transistors are characterized by associated ideal maximum permissible cross terminal voltages, and such voltages are generally referred to as the voltage specification for the corresponding transistors. For example, it is generally desirable to keep the ideal maximum cross terminal voltage of a 1.8V transistor below 1.8V, even though up to 2.4V is often applied across the terminals of the 1.8V transistor, in which case there is some exposure to reducing the life-time of the transistor, etc. The 2.4V limit may be referred to as allowed maximum voltage.
It is often desirable to implement high voltage circuits using transistors (“low voltage transistors”) of low(er) voltage specification. In general, using low voltage transistors provides benefits such as high throughput performance, reduced electrical power consumption, and high density (number of integrated circuits in a unit area). What is therefore needed is a method and apparatus to implement high voltage circuits using low voltage transistors.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.